1. Field of the Invention
This invention relates to conductive compounds and, in particular, carbonaceous conductive compounds.
2. Art Background
Recently there has been significant interest in organic materials that are either conductive or that can be doped to produce conductivity. Such organic materials have been suggested for a wide variety of uses that depend on their conductivity. For example, organic materials are generally easily formed in thin films as conductive components in devices such as switches, antistatic devices or magnetic shielding.
The classic carbon-based conductors are graphite and polyacetylene. (Graphite is characterized by an infinite sheet-like structure of the element carbon.) Graphitic materials typically have conductivities in the range 10.sup.3 to 10.sup.5 Siemens/cm, but are intractable and therefore for some applications do not lend themselves to fabrication of the desired devices. Polyacetylene when doped has conductivities as high as 10.sup.4 Siemens/cm, but can be processed only during its preparation. Other organic conductors, such as those based on tetrathiafulvalene, have high conductivities (10.sup.3 Siemens/cm), but again are difficult to form into desired geometries. (See, for example, U.S. Pat. No. 4,249,013 dated Feb. 3, 1981.)
A class of nascent organic materials are those based on fullerenes. Such materials are prepared by an electronic discharge process as described in Kroto, H. W. et. al., Nature 318, 162 (1985) and Kratschmer, W. et. al., Nature 347, 354 (1990). These materials, as reported, are insulators. Attempts have been made to modify these materials to improve their conductivity. For example, as reported by Wudl, F. at the Materials Research Society Meeting, Nov. 29, 1990, Boston, Mass., a tetraphenylphosphonium salt of fullerene has been made, but exhibited a conductivity no greater than 10.sup.-5 Siemens/cm. Generally for most applications, conductivities greater than 10.sup.-4 Siemens/cm, preferably greater than 10.sup.-3 Siemens/cm, most preferably greater than 0.1 Siemens/cm, are desired.
Thus, although a substantial body of research has been directed to tractable carbonaceous compounds having reasonable conductivities, such research has not been entirely successful.